Force and energy dissipation variations in noncontact atomic force spectroscopy of composite carbon nanotube systems

UHV dynamic force and energy dissipation spectroscopy in noncontact atomic force microscopy were used to probe specific interactions with composite systems formed by encapsulating inorganic compounds inside single-walled carbon nanotubes. It is found that forces due to nanoscale van der Waals interaction can be made to decrease by combining an Ag core and a carbon nanotube shell in the silver-filled single-walled carbon nanotube (Ag@SWNT) system. This specific behavior was attributed to a significantly different effective dielectric function compared to the individual constituents, evaluated using a core-shell model. Energy dissipation measurements showed that by filling dissipation increases. Aside from minimized Joule dissipation, such an effect was attributed to two short-range mechanisms due to metal filling: softening of C-C bonds resulting in a more deformable nanotube cage, and an increased mechanical damping of the nanotube's bending oscillation mode. Thus, filled and unfilled nanotubes can be discriminated based on force and dissipation measurements. These findings have two different implications for potential applications: tuning the effective dielectric properties and tuning the interaction force for molecular absorption by appropriately choosing the filling with respect to the nanotube.